This invention relates generally to an alignment system and an alignment method. More particularly, the invention concerns an alignment system and an alignment method for use in a semiconductor manufacturing exposure apparatus, for performing a relative positioning (alignment) of a fine electronic circuit pattern (such as an IC, an LSI or a VLSI) formed on the surface of a reticle (first object) and a wafer (second object).
Currently used exposure apparatuses are mainly those called a stepper and those called a scanner. In this specification, however, for convenience, all of them are simply referred to as xe2x80x9cexposure apparatusxe2x80x9d, except in cases where they should be distinguished.
In another aspect, the invention is directed to a method for optimum use of an exposure apparatus, which is based on data communication between a place where the exposure apparatus is present (such as a semiconductor factory) and a place remote therefrom (e.g., a vendor such as a manufacturing apparatus maker or a consultation company), through an internet.
In order to meet further decreases in size and further increases in density of an integrated circuit, projection exposure apparatuses for manufacture of semiconductor devices are required to have an ability of projecting a circuit pattern of a reticle and printing it upon the surface of a wafer, with a high resolving power. Since the projection resolution of a circuit pattern depends on the numerical aperture (NA) of a projection optical system and the exposure wavelength (the wavelength used for the exposure), various exposure methods have been attempted such as, for example, an exposure method in which the NA of a projection optical system is enlarged while the exposure wavelength is fixed, and an exposure method in which the exposure wavelength is shortened such as, for example, from g-line to i-line, from i-line to an excimer laser emission wavelength, or, even in the excimer laser emission wavelength, to 248 nm, 193 nm and to 157 nm. As regards the exposure wavelength of 193 nm, commercial products are already available-
On the other hand, due to decreases in size of circuit patterns, there is a requirement for high precision alignment of a reticle (having an electronic circuit pattern) and a wafer. Alignment errors may be generally categorized into an apparatus factor and a process factor. Recently, errors attributable to any apparatus factor are well corrected, as much as possible. As regards errors attributable to any process factor, called WIS (Wafer Induced Shift), an alignment detecting system which can meet this has been proposed by the same assignee of the subject application, as an offset analyzer system.
First, as an example of WIS, due to a process error factor, the shape of an alignment mark or the shape of a resist on that mark becomes asymmetric. During a flattening process in a recently introduced metal CMP (Chemical Mechanical Polishing) process, for example, the structure of an alignment mark frequently becomes asymmetric. This causes, in a global alignment process, a rotational error (FIG. 1A) or a magnification error (FIG. 1B) which directly leads to a deteriorated precision. Here, FIG. 1A illustrates a case where rotational errors are produced in a global alignment process. FIG. 1B shows a case where magnification errors are produced in a global alignment process. Straight lines in these drawings depict the direction and amount of the errors produced.
In an offset analyzer such as mentioned above, for relative alignment of a wafer and a reticle, the position of the wafer is detected by use of an alignment system of a non-exposure light TTL off-axis system having a stable baseline. Prior to this detection, as regards plural but the same marks formed on the wafer for use in the alignment process, the surface shape thereof before and after resist application is measured (at calibration, for example), outside the alignment system (exposure apparatus) and by use of a profiler (solid shape measuring device) such as an AFM (Atomic Force Microscope), for example. Then, an offset, when the three-dimensional relative positional relationship between the resist and the wafer mark is harmonized with a signal of a detecting system of the alignment system, is calculated. The alignment operation is made by using the calculated value. Through the procedure described above, degradation of precision due to the produced symmetry in the alignment mark shape can be avoided.
This is the system called an offset analyzer, in which, outside the alignment system (exposure apparatus), the surface shape is measured before and after resist application, by using a profiler such as an AFM, and in which an offset, as the three-dimensional relative positional relationship between the resist and the wafer mark is harmonized with the signal of a detecting system of the alignment system, is calculated.
FIG. 1C shows the results of measurement of actual alignment marks, made by use of an AFM. Signals are those after resist application. The structure of the alignment marks is such as called a metal CMP, as shown in FIG. 1D. FIG. 1D illustrates the structure of an alignment mark, called a metal CMP. It is seen from FIG. 1C that, as regards the shape of a resist upon alignment marks at left and right side shots as well as an alignment mark at a central shot, the surface shape at the central shot is symmetric whereas the surface shape at the left and right side shots is asymmetric. Also, it is seen that the asymmetry is inverted, between the left and right side shots. This is what called WIS. The WIS can be met by use of an offset analyzer, and high precision and a stable alignment method with a small baseline change can be accomplished.
Referring to FIGS. 1E and 1F, an already proposed offset analyzer will be explained. FIG. 1E is a schematic view for explaining the flow of a wafer and information where an offset analyzer is provided. FIG. 1F shows the structure of the offset analyzer.
Here, as described hereinbefore, a stepper, a scanner, an aligner or the like is called an exposure apparatus. An alignment detecting system is called an alignment scope. A system in which the surface shape is measured before and after resist application, outside an alignment system (exposure apparatus) and by use of a profiler and in which an offset as the three-dimensional relative positional relationship between the resist and the wafer is harmonized with the signal of a detection system of the alignment system, is called an offset analyzer.
Referring to FIG. 1E, the flow of a wafer and information will be described first.
In this example, as shown at step 2 in FIG. 1E, a wafer 31 is conveyed to an offset analyzer 32 before a resist is applied thereto. The shape (surface shape) of an alignment mark on the wafer 31 is measured by using a profiler.
Then, at step 3 in FIG. 1E, the wafer 31 is conveyed to a coater 33 for resist application, and a resist is applied to the wafer.
Then, at step 4 in FIG. 1E, the wafer 31 is conveyed again to the offset analyzer 32, and the surface shape of the resist on the alignment mark is measured by using the profiler.
Subsequently, a signal for the alignment mark on the wafer 31 is detected by use of a detecting system installed in the offset analyzer 32 and being similar to an alignment scope of the exposure apparatus.
Then, by use of a signal simulator of the offset analyzer 32, an offset is calculated. For this offset calculation, a three-dimensional relative positional relationship between the resist and the wafer mark should be harmonized. Specifically, while changing the three-dimensional relative positional relationship between the resist and the wafer mark, the relationship with which the result of the signal simulator is registered with the alignment mark signal, is taken as the three-dimensional relative positional relationship between the resist and the wafer mark. By using the relative positional relationship at that time, an alignment signal is obtained and, from it, an offset for alignment measurement is calculated. The resultant value is supplied to an exposure apparatus (stepper) 35.
On the basis of this offset, the exposure apparatus (stepper) 35 performs an alignment and exposure process (step 5). After exposures of all shots are completed, the wafer 31 is conveyed to a developer 36, and a developing process is performed there (step 6 in FIG. 1E).
Next, referring to FIG. 1F, the structure of the offset analyzer 32 (FIG. 1E) will be explained.
The offset analyzer 32 comprises a chuck 41 for supporting a wafer 31, an X-Y-Z stage for moving the water three-dimensionally, a profiler 43 for performing surface measurement with or without a resist, a detecting system 44 equivalent to an alignment scope provided in the exposure apparatus 35 (FIG. 1E), and a CPU 45 for controlling the offset analyzer 32 as a whole and having a simulator 46 for calculating an alignment offset (an offset amount in the alignment measurement) from the surface shape. A wafer conveying system and a focusing system for the wafer 31 are not illustrated.
Here, an apparatus error (TIS: Tool Induced Shift) of the alignment scope of the exposure apparatus 35 and the offset analyzer 32 should be controlled, or it should be detected. For example, coma aberration of the optical system or non-uniformness of the illumination system corresponds to it.
The alignment scope of the exposure apparatus 35 may be adjusted so that the error can be disregarded. Alternatively, the alignment scope of the exposure apparatus 35 and the alignment detecting system of the offset analyzer 32 may be adjusted to have the same error.
As a method of estimating such TIS, an example has been proposed in Japanese Laid-Open Patent Application, Laid-Open No. 280816/1997.
When the apparatus error information about the alignment scope of the exposure apparatus 35 is predetected, the offset analyzer 32 may not have an alignment detecting system equivalent to the alignment scope of the exposure apparatus 35. For example, the offset analyzer 32 may not have an alignment detecting system equivalent to the alignment scope of the exposure apparatus 35. For example, the offset analyzer 32 may be equipped with a bright field detecting system, while the exposure apparatus may be provided with a dark field detecting system. The offset amount may be calculated while taking into account this error, by using the simulator 46.
The offset analyzer 32 is provided separately from the exposure apparatus 35, which is an exposure machine. With respect to the throughput, it is effective to provide plural offset analyzers in association with plural exposure apparatuses 35 (the number may be different) such that the alignment offset can be calculated in a sequence which does not interfere with the exposure operation in the exposure apparatus.
As described, by measuring an alignment mark and by calculating an offset, to be produced thereby, beforehand, deterioration of precision due to a produced symmetry in the alignment mark shape can be prevented. Thus, a high precision and high throughput alignment method are accomplished.
The offset analyzer described above may be used for all wafers. Alternatively, it may be used in a sequence for a first wafer in restricted conditions. The obtained offset may be used for wafers following the first wafer.
Use of the offset for the wafers following the first wafer is limited to a case where, under restricted conditions (e.g., wafers in a certain lot), the asymmetry in the shape of alignment marks of the wafers has a small dispersion.
As described above, a sequence in which an offset analyzer is used at least once is possible.
As explained above, in a sense of meeting WIS, an offset analyzer can be very effective. However, in the exposure system as a whole, it needs addition of an offset analyzer.
Particularly, in the offset analyzer, an alignment signal is obtained by signal simulation using a simulator, and a measurement error is then calculated from the obtained signal. Each offset analyzer needs a simulator and a computer for driving it. For high speed operation, expensive computers capable of performing high speed calculation must be provided in each exposure system.
It is an object of the present invention to provide at least one of an adjusting system for an exposure apparatus, an alignment system, an alignment method, a data processing system and a device manufacturing method using one of them, by which an unwanted increase of the apparatus cost can be prevented while retaining the function of an offset analyzer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.